The present invention relates to a sustained release formulation of etodolac for once daily administration.
Etodolac (1,8-diethyl-1,3,4,9-tetrahydropyrano [3,4-b] indole-1-acetic acid or a therapeutically acceptable salt thereof) is disclosed in U.S. Pat. No. 3,939,178. It has been reported to have analgesic and anti-inflammatory properties. It has also been reported to be effective in the treatment of gout by lowering uric acid blood levels in humans (U.S. Pat. No. 4,663,345) and in the treatment of rheumatoid arthritis by lowering rheumatoid factor blood levels (U.S. Pat. No. 4,742,076).
Etodolac is approved for the management of signs and symptoms of osteoarthritis, rheumatoid arthritis and for the management of pain. The conventional dosing regimen is 800 mg to 1200 mg given in 2-4 divided doses. This regimen can cause problems of compliance due to lack of patient convenience. It is well known to those skilled in the art that sustained release systems result in a decrease in frequency of administration thereby improving patient compliance. Furthermore, sustained released drug delivery systems produce constant therapeutic plasma levels of active ingredients as compared to fluctuations seen with multiple doses of a conventional formulation. However, development of a sustained release formulation of etodolac effective for 24 hours or suitable for once-a-day administration poses problems due to a very low aqueous solubility of Etodolac which is pH independent below pH 3. The solubility then gradually increases with increasing pH up to 5 and then linearly increases with increasing pH up to 7. A thirty-fold difference between solubility at pH 5 to pH 7 has been observed.
The problem of poor solubility of Etodolac in the acidic media has been addressed by Michelucci et al. by the addition of a release rate modifying agent for maintaining an alkaline microenvironment pH within the tablet. U.S. Pat. No. 4,966,768 describes a sustained release dosage form of Etodolac for once-a-day administration. The addition of a release rate modifiers ensures that pH dependent solubility is minimized throughout the gastrointestinal tract. An admixture of a hydrophilic polymer, hydroxypropyl methylcellulose and a hydrophobic polymer, ethyl cellulose is used for sustaining the release of the drug from the dosage form. The use of a hydrophobic polymer retards the dissolution of the poorly soluble and hydrophobic drug, etodolac, in acidic media thus necessitating the use of release rate modifiers.
U.S. Pat. No. 4,704,285 discloses the use of fine particle sized hydroxypropyl cellulose ether composition for delaying the release of the active composition from a tablet longer upon contacting an aqueous acidic environment at 37xc2x0 C. compared to a chemically identical but coarser particle sized hydroxypropyl cellulose ether composition. This formulation is not suitable for drugs like etodolac which are poorly soluble in the acidic media.
An object of the present invention is to provide a sustained release dosage form of etodolac suitable for once daily administration comprising a carrier base material which comprises only hydrophilic polymers wherein no release rate modifying agents are present.
In accordance with the present invention, there is provided a sustained release dosage form suitable for once-a-day administration of Etodolac comprising etodolac and a carrier base material, wherein the carrier base material comprises one or more multiple viscosity grades of a hydrophilic polymer such as hydroxypropyl cellulose.
The etodolac used in the present invention is preferably micronized to increase its total surface area and improve its solubility. Hydroxypropylcellulose (HPC) is a partially substituted poly (hydroxypropyl) ether of cellulose which is commercially available under the trade names Klucel(trademark) (Aqualon), Methocel(trademark) (Dow Chemical Co.), and Nisso HPC(trademark). In accordance with the present invention, the carrier base material preferably comprises one or more viscosity grades of HPC. More preferably, hydroxypropyl cellulose is selected from the viscosity grades of 6.0 to 10.0 centipoise (HPC-L) and 150-400 centipoise (HPC-M) for a 2% aqueous solution at 20xc2x0 C. HPC-L is present from about 5-40% w/w of the formulation or more preferably from 5-20% w/w of the formulation and HPC-M is present from about 5-25% w/w of the formulation or more preferably from 5-15% w/w of the formulation. HPC-L is a rapidly swellable material and is responsible for controlling the initial release of the drug from the dosage form. HPC-M controls the rate of drug release over an extended period of time. It is the appropriate ratio of the two polymers that provides the desired in vitro profiles and the once daily pharmacokinetic profiles. The combined proportion of the carrier base material in the dosage form of the invention can range from 5-65% by weight or more preferably from about 10-35% by weight.
According to the present invention, the pharmaceutical composition may additionally contain conventional pharmaceutical excipients such as diluents, binders, disintegrants, lubricants, coloring agent, etc. According to a preferred embodiment of the present invention, lactose is used as the filler and polyvinyl pyrrolidone (PVP) as the binder.
According to invention, the pharmaceutical composition is preferably in the form of tablets. The tablet is preferably film coated.